The present invention generally relates to a purification apparatus and more specifically, to a hydrogen gas purification apparatus utilizing hydrogen absorbing-desorbing alloys such as titanium-manganese alloy systems, etc.
Generally, hydrogen gas is important, for example, as a raw material, for industrial purposes, and is employed in a large quantity in various industries, for example, for synthesis of ammonia, methanol and the like or for purification of petroleum. Meanwhile, production of hydrogen gas which plays an important role in these modern industries is mainly effected by electrolysis of water, decomposition of ammonia, hydrocarbon (natural gas, petroleum, etc.), and methanol.
Hydrogen gas to be manufactured by the processes as described above generally contains inactive rare gases such as helium, krypton, argon and the like, inorganic group gases such as oxygen, nitrogen, carbon monoxide, carbon dioxide, ammonia, water, etc. and organic gases such as methane, ethane, etc. Accordingly, it becomes necessary to purify raw hydrogen gas according to end uses thereof.
At present, for the purification of raw hydrogen gas, there are commonly employed the absorption process, adsorption process, diffusion process, deep freeze separation process, chemical reaction process, etc., among which the adsorption process and diffusion process are particularly frequently employed as the methods capable of yielding hydrogen of high purity.
The adsorption process is the purification method of raw hydrogen gas most commonly employed today, and is arranged to remove impurities in the raw hydrogen gas by causing them to be adsorbed to zeolite group adsorbents, or adsorbents such as active carbon, alumina, silica gel and the like. The adsorption process is further classified into the pressure cycle system adsorption method, temperature cycle system adsorption method, and deep freeze adsorption method, etc. The pressure cycle system adsorption process is adapted to utilize a pressure cycle at normal temperature for effecting adsorption and desorption of impurities by the pressure difference. The temperature cycle system adsorption process utilizes a heating-cooling cycle for carrying out purification of raw hydrogen gas by the temperature difference. Meanwhile, in the deep freeze adsorption method, ultra-low temperature as in liquefied nitrogen (-196.degree. C.) is utilized for purifying raw hydrogen gas by causing impurities to be adsorbed in the adsorbents.
On the other hand, the diffusion process utilizes a thin film layer of palladium-silver alloy so as to cause only hydrogen to diffuse and permeate therethrough for separation of hydrogen from impurities which can not pass through said thin film layer.
However, the conventional purification processes as described above have disadvantages as follows. In the first place, the adsorption process requires a cooling source such as liquefied nitrogen and the like, with complicated operations, thus resulting in high cost for hydrogen gas purification. Moreover, since removal of water content and carbon dioxide gas is essential as a preliminary treatment, the purification process is further complicated. Furthermore, in the known diffusion process as described earlier, not only is there some problem in the durability of the palladium-silver alloy layer, but the purification arrangement itself is comparatively expensive owing to the employment of such precious metals.
Meanwhile, there has been proposed, for example, in U.S. Pat. No. 3,516,263, a process for purification of hydrogen through utilization of metal hydrides, by which it is known that, since the alloy for absorbing hydrogen absorbs only hydrogen in hydrogen gas containing impurities, and desorbs only hydrogen, the hydrogen gas desorbed from the hydrogen absorbing alloy becomes much higher in purity than the hydrogen gas at the time of absorption. In this prior art hydrogen gas purification process employing the hydrogen absorbing alloy, absorption of hydrogen is effected through heat generation or exothermic reaction and desorption thereof is effected through heat absorption or endothermic reaction as is seen from the following reaction formula. ##STR1## where M is alloy, MH.sub.2 is hydride and Q is heat.
Therefore, the above known process, is arranged to take out hydrogen gas from a hydrogen storage container through heating for desorption of hydrogen, and cooling for absorption thereof. However, this prior art process requires separate heating and cooling sources, and when the heat source is not used, internal pressure is lowered due to the endothermic reaction during desorption of hydrogen, resulting in a reduction of flow rate, and thus, purified hydrogen gas can not be taken out continuously.